Knock Control, Function - GF07.10-P-1015MRA

Engine 274.9 in model 205 (except 205.047/053/054/147/247/253) 

Engine 274.9 in model 253 (except 253.354/954) 

Function requirements for knock control, general points 

• Circuit 87M (Engine management ON)
• Engine runs

Knock control, general points 

The knock control is integrated in the ME-SFI [ME] control unit (N3/10) and has the task is to ensure knock-free engine operation under all operating conditions and when different fuel grades are used. In the case of uncontrolled combustion (knocking), the ignition angle of the ignition coils for cylinder 1 to ignition coils for cylinder 4 (T1/1 to T1/4) for the related cylinder is adjusted towards "retard".

The ME-SFI [ME] control unit manages the knock control according to the following signals:

• Knock sensor 1 (A16/1)
• Knock sensor 2 (A16/2)
• Intake camshaft Hall sensor (B6/15), intake camshaft position (ignition circuit detection)
• Exhaust camshaft Hall sensor (B616), exhaust camshaft setting (ignition circuit detection)
• Coolant temperature sensor (B11/4)
• Charge air temperature sensor upstream of throttle valve (B17/7)
• Charge air temperature sensor downstream of throttle valve (B17/9)
• Pressure sensor downstream of throttle valve (B28/7), engine load
• Accelerator pedal sensor (B37), load request by driver
• Crankshaft Hall sensor (B70), engine speed and crankshaft position (ignition circuit detection)
• RON default setting (R  esearch O  ctane N  umber) with Xentry Diagnostics

The requirements of the torque coordination function are also taken into account.

Function sequence for knock control 

The function sequence is described in the following steps:

• Function sequence for ignition angle setting 
• Function sequence for RON correction 
• Function sequence for knock control adaptation 
• Function sequence for knock identification error 

Function sequence for ignition angle setting 

Knock control is enabled under the following operating conditions:

• Coolant temperature > 30°C
• Engine load > 34%

According to its input signals, the ME-SFI [ME] control unit computes the cylinder-specific ignition angle correction.

If knocking is detected in a cylinder by the knock sensors, the cylinder's ignition angle is adjusted towards "retard" at the next ignition (dependent on engine speed). If knocking continues to occur, the ignition angle is adjusted further towards "retard", and so on until maximum adjustment is reached.

If knocking-free combustion exists, the retarding the ignition timing is reduced in stages after a few ignitions (depending on engine speed) until the normal characteristics map value is achieved or knocking once again occurs.

Function sequence for RON correction 

The RON correction can be preset using Xentry Diagnostics by means of correction programming.

Knock control is also fitted out with an automatic RON switch. This detects a persistent high tendency to knock of the engine and assists the knock control by means of an appropriate pre-control.

This is done by evaluating the stored adaptation values, the ignition angle of all the cylinders and the number of control interventions in certain engine load and speed ranges.

The RON stage is adjusted by one or several stages depending on the threshold which has been exceeded. The regulated RON stage remains until stopping of the engine.

The higher the RON stage selected, the lower the maximum retarding the ignition timing of the ignition angle.

Function sequence for knock control adaptation 

Adaptation by the knock control becomes active starting from a coolant temperature of about 75°C.

The ignition angle corrections required due to combustion knocking are stored continuously for the specific cylinder, along with the related operating condition of the engine (engine load and engine RPM).

When determining the individual ignition angles, the stored adaptation values are taken into account, so that the optimal ignition angle can be calculated immediately for each cylinder.

Function sequence for knock identification error 

For safety reasons, if one of the knocking sensor signals fails, the ignition angles of all cylinders is retarded by up to 12° crank angle (according to engine speed and coolant temperature). Knock control and the adaptation are deactivated and a fault is stored in the fault memory.

The ignition angle corrections of the thermal management and the knock control are added based on the performance map.

	Electrical function schematic for knock control		PE07.10-P-2715-97FBA
	Overview of system components for gasoline injection and ignition system with direct injection		GF07.70-P-9998MRA